1. Field of the Invention
This invention relates to single strand modular rolling mills for rolling long products such as bars, rods and the like.
2. Description of the Prior Art
With reference initially to FIG. 1, a known modular rolling mill of the type described in the commonly assigned U.S. Pat. No. 5,595,083 is shown comprising at least three, and in this case, five rolling units RU.sub.1 -RU.sub.5 arranged in succession on a mill pass line P.sub.L. Each rolling unit has multiple pairs of work rolls 10a, 10b. The work rolls may be sized and grooved to provide a typical oval-round pass sequence, with successive roll pairs being offset by 90.degree. to effect a twist-free rolling sequence on a product being directed along the mill pass line.
Except for the size and/or groove configuration of the work rolls, the rolling units are identical and interchangeable one for the other at any location along the mill pass line. With reference to FIG. 2, which is a diagrammatic illustration of the internal drive components of a typical rolling unit, it will be seen that the work rolls 10a are mounted in cantilever fashion on the ends of roll shafts 12 rotatably supported by bearings 14. Gears 16 on the roll shafts mesh with intermeshed intermediate drive gears 18, the latter being carried on intermediate drive shafts 20 journalled for rotation between bearings 22. The work rolls 10b are mounted and driven by mirror image components identified by the same reference numerals. One of each pair of intermediate drive shafts 20 is additionally provided with a bevel gear 24 meshing with a bevel gear 26 on an input shaft 28. The input shafts 28 protrude from a "drive side" of the rolling unit where they terminate in coupling halves 30a.
The two input shafts are additionally provided with gears 32 which mesh with a larger diameter intermediate gear 34. It will thus be seen that the work roll pairs 10a, 10b of each rolling unit are mechanically interconnected as a result of the interengagment between the gears 32 on the input shafts 28 and the intermediate gear 34.
Returning to FIG. 1, it will be seen that drive units DU.sub.1 -DU.sub.4 are arranged in succession alongside the mill pass line PL. Each drive unit includes a gear box 36 driven by a drive motor 38. The gear boxes have gear connected output shafts 40 terminating in coupling halves 30b. It will be understood that the coupling halves 30a on the input shafts 28 of the rolling units are designed to mate with the coupling halves 30b on the output shafts 40 of the gear boxes 36 to provide readily separable drive connections, thereby accommodating ready engagement and disengagement of the rolling units from the drive units. The input shafts 28 of each of the rolling units RU.sub.2, RU.sub.3, RU.sub.4, i.e., all but the first and last rolling units, are coupled to the output shafts 40 of two successive drive units DU.sub.1 -DU.sub.4. The first and last rolling units RU.sub.1, RU.sub.5 are coupled respectively and exclusively to the first and last drive units DU.sub.1, DU.sub.5.
It will thus be seen that the drive units DU.sub.1 -DU.sub.4 are coupled one to the other via the internal drive components of the rolling units RU.sub.1 -RU.sub.5 to thereby provide a continuous drive train from one end to the other of the modular mill. With this arrangement, as the front end of a product enters each successive roll pass, the resulting momentary speed decrease is transmitted throughout all of the rolling units, thereby making it possible to maintain substantially constant interstand product tension in a self regulating manner without resort to external controls. This continuous drive train drives the successive work roll pairs at progressively higher speeds as depicted graphically in FIG. 3.
Modular rolling mills of the above described type are widely used to roll low, medium, high carbon and low alloy steel products, where the heat build-up between roll pairs is relatively modest. For example, when rolling a 16.8 mm process section into a 5.5 mm rod at delivery speeds of 100 m/sec, heat build-up between the first and last roll pairs of the modular mill is likely to be on the order of 100 to 150.degree. C. However, more exotic products, e.g., nickel based alloys, high speed steels, waspalloys, etc. cannot tolerate such temperature increases. Since there is insufficient space between the rolling units to accommodate sufficient water cooling, up to now one option has been to substitute water boxes for selected rolling units. While this provides added cooling, it does so by sacrificing the continuity of the drive train.
Another option has been to reduce the rolling speed of the mill in order to reduce energy build up in the product being rolled. This too is unsatisfactory because it results in a reduction in the output of the mill. Lower temperature thermomechanical rolling has also been difficult to achieve, again due to the inability to introduce adequate cooling between the successive rolling units.
The objective of the present invention is to provide a gap in the rolling sequence of the modular mill in order to accommodate the introduction of additional cooling, without interrupting the continuity of the drive train.